This invention concerns a process for regenerating certain noble metal catalysts used in the carbonylation, hydroformylation and hydrogenation of olefins. Carbonylation refers here to the reaction of an olefin with carbon monoxide and an active-hydrogen-containing compound selected from the group consisting of an alkanol or water. This reaction is exemplified in eq. 1, wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4, individually, are hydrogen, alkyl up to 12 carbon atoms, alkenyl of up to 12 carbon atoms, or aryl up to 12 carbon atoms, or mixed alkyaryl or arylalkyl groups. ##STR1##
Suitable alkanols (ROH) include primary and secondary alcohols of 1 to 12 carbons, phenols, substituted alcohols and polyols. The major products of carbonylation are fatty (carboxylic) acids and their esters.
Hydroformylation is conducted by the reaction of a mixture of olefin, carbon monoxide and hydrogen, in the presence of a suitable catalyst. The process of hydroformylation may be expressed by eq. 2, wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are defined as above. The major products are aldehydes or alcohols. ##STR2##
The preparation of the fatty acids or fatty esters using metal carbonyls or carbonyl precursons to catalyze the carbonylation of olefins (eq. 1) is old in the literature, originally involving Reppe and his coworkers and contemporaries. Reviews by C. W. Bird [Chem Rev. 62, 283 (1962)] document this work. Unfortunately, many of these carbonyl-type catalysts have the disadvantages of inherent toxicity, they require stringent reaction conditions which in turn lead to competing side reactions such as olefin isomerization, polymerization and reduction, and they exhibit poor selectivity to the desired linear acid ester.
Recently, more acceptable homogeneous catalyst systems have been developed which offer substantially improved selectivity in converting olefins to primarily linear fatty acids or linear fatty esters, in good yield, under moderate reaction conditions of temperature and pressure.
As is usually the case, after much more extensive usage, certain drawbacks have become more evident. These include difficulty in maintaining high conversions, high selectivities and high yields after recycling the catalyst several times. These problems are due to catalyst degradation as well as catalyst decomposition, mechanical losses and further catalyst decomposition during the separation of the products from the homogeneous catalysts and the inert solvents of the reaction mixture. Thermal instability of the catalyst is particularly troublesome in the recovery and working-up of certain ligand-stabilized homogeneous palladium catalyst reaction mixtures.
In order to avoid or minimize these problems, the use of molten quaternary ammonium, phosphonium and arsonium salts of trihalostannate(II) and trihalogermanate(II) as both solvent and part of the catalytic entity has been disclosed, particularly in the two U.S. Pat. Nos. of G. W. Parshall, 3,657,368 and 3,565,823 which are believed to be the closest known art except for applicant's more recently filed Ser. No. 526,867 filed 11/25/74 in the U.S. Patent Office.
However, in order to develop a commercially acceptable regeneration catalytic process it is necessary to demonstrate several key positive advantages:
1. A simple and efficient means of separating catalyst from the products,
2. The ability to recycle the catalyst without its substantial deactivation. This is particularly important in the case of the thermally sensitive palladium catalysts.
3. Regeneration processes which are capable of restoring the activity of the deactivated catalyst, particularly at high concentrations of catalysts up to 0.1 mole % concentration in the feed.
In this application are disclosed two different illustrative procedures for isolating organic products such as are produced by olefin carbonylation, hydroformylation and hydrogenation. These organic products may be separated in high purity from the palladium and platinum catalysts consisting of dispersions of ligand-stabilized palladium(II) halide and platinum(II) halides in quaternary ammonium, phosphonium and arsonium salts of trihalostannate(II) and trihalogermanate(II) by the procedures disclosed infra, and the palladium or platinum catalysts recycled with fresh olefin feed. The most important aspect of this application is the claimed process for restoring the activity of the above mentioned spent catalyst dispersions of the palladium(II) or platinum salts in quaternary ammonium, phosphonium and arsonium salts of trihalostannate(II) and trihalogermanate(II) by the treatment described below.